Bright,level tin plating



United States Patent 3,479,259 BRIGHT, LEVEL TIN PLATING Raymond F. Nambride, Paris, France, assignor to Enthone Incorporated, New Haven, Conn., a corporation of Connecticut No Drawing. Filed Oct. 2, 1967, Ser. No. 671,986 Claims priority, application France, Dec. 30, 1966,

89,625 Int. C1. C23!) 5/46, 5/14 US. Cl. 20454 14 Claims ABSTRACT OF THE DISCLOSURE This invention concerns improved aqueous acid tin electrodepositing baths containing, as a brightening and levelling agent, a cyclohexylsulfamate.

BACKGROUND OF THE INVENTION Field of the invention Description of the prior art Tin electroplating baths are known in the prior art which contain stannous sulfate, sulfuric acid and orthocresolsulfonic acid as brightener and grain refiner. These prior acid tin baths have given tin electrodeposits of satin lusters, and prominent among such prior art tin plating baths were those containing about 50-100 g./l. of stannous sulfate, about -50 ml./l. of 66 B. sulfuric acid and about 10-50 g./l. of orthocresolsulfonic acid.

Tin electroplating baths containing sulfamic acid and stannous ions are also known in the prior art. Such baths can also contain an additive compound such as di-, trior tetramethyl dihydroquinoline, dihydroxydiphenylsulfone, bisparahydroxyphenyl propane or dihydroxybenzophenone. The sulfamic acid is not a brightener but is employed in the baths to provide conductivity and to keep the tin salts dissolved. The additive compound serves to brighten the electrodeposited tin only upon re-flowing of the tin by heating the base metal upon which the tin layer is deposited to melt the tin. However this re-fiowing of the tin electrodeposit at elevated temperatures to brighten the tin poses insurmountable problems in the plating of substrates or surfaces which are thermally degradable or unstable at the elevated temperatures of the melting, for instance the typical polymer insulating boards or bases of printed circuit boards which are ruined at the melting temperatures of the tin. Further the melting reflowing to brighten the tin is time consuming and may add appreciable additional expense to the plating operation.

SUMMARY OF THE INVENTION The aqueous acid tin electrodepositing bath of the present invention comprises an aqueous acid bath containing a bath-soluble tin salt and an effective amount, suificient to yield a bright, level tin electrodeposit, of a cyclohexylsulfamate. When the cyclohexylsulfamate is present in the acid bath as a secondary brightener and levelling agent together with a suitable known primary brightener and grain refiner such as, for example, the orthocresolsulfonic acid of the prior art baths first mentioned herein, very bright and levelling tin electrodeposits are attained and which are a considerable im- ICC provement in brightness and levelling over the tin electrodeposits obtained from such prior tin plating baths containing the cresolsulfonic acid as sole brightening agent. Further the acid tin electrodepositing baths containing the cyclohexylsulfamate of this invention do not require melting and re-fiowing of the tin electrodeposit for brightness as required by the prior art tin electroplating baths containing sulfamic acid and the additive compound, and thus can be utilized to plate boards, bases or surfaces of low thermal stability and which would be detrimentally affected or ruined by the elevated temperatures required to melt tin.

The cyclohexylsulfamate herein when used as sole brightener in the acid tin electrodepositing bath will impart brightness and levelling to the tin deposit. However the cyclohexylsulfamate is preferably utilized in the tin plating bath of this invention as a secondary brightener and leveller in combination with a primary brightener and grain refiner, for example a cresolsulfonic acid or a phenolsulfonic acid. The use of the cyclohexylsulfamate as sole brightener in the bath tends to result in a brittle, excessively stressed tin deposit and the brittleness and excess stress is eliminated by the combination of the primary and secondary brighteners,the primary brightener functioning as a grain refiner as well as a brightener.

The cyclohexylsulfamate is either cyclohexylfamic acid and/or a bath-compatible water soluble salt thereof. The cyclohexylsulfamate has the formula @avusom wherein M is a hydrogen atom or a bath-compatible water solubilizing cation. Exemplary of the bath-com patible solubilizing salt-forming cations are alkaline cations, for instance alkali metal cations, for example Na+ or K+, and alkaline earth metal cations such as Ca++. M can also be divalent tin, i.e. Sn++, and Sn++ is included within the scope of the term bath-compatible water-solubilizing cation as used herein. It is to be understood that any cation can be utilized herein as M which is bath-compatible and function to impart water solubility to the compound. By bath-compatible as used herein in describing the cation is meant a cation which will not substantially detrimentally or adversely affect the acid tin electrodepositing bath or interfere substantially with the electrodeposition of a bright, level tin from the bath. The foregoing examples of the cyclohexylsulfamates include cyclohexylsulfamic acid, sodium cyclohexylsulfarnate, potassium cyclohexylsulfamate, calcium cyclohexylsulfam-ate and stannous cyclohexylsulfamate. The cyclohexylsulfamates wherein M is the bath-compatible, water-solubilizing cation are preferred for use herein.

The cyclohexylsulfamates herein can be prepared by hydrogenating a phenylsulfamate of the formula Q-NHSOaM wherein M has the meaning aforesaid, with gaseous hydrogen in the presence of ruthenium as catalyst at a temperature between about 60 C. and about C. and a pressure in excess of 100 p.s.i. until 3 moles of hydrogen are absorbed or reacted. The phenylsulfarnic acid and phenylsulfamates can be prepared by prior art methods such as are disclosed by L. F. Audrieth and M. Sveda in J. Org. Chem., vol. 9, pp. 89-101, 1944. The alkali metal cyclohexylsulfamate is also readily obtainable in commerce.

Exemplary of the bath-soluble tin salts are water-soluble stannous salts of inorganic acids such as of mineral acids, for example stannous sulfate and stannous chloride, or of the non-mineral inorganic acid fluoboric acid, e.g. stannous fiouborate.

The acid tin electrodepositing baths herein contain acid in suitable quantity, usualy a mineral acid, although the non-mineral inorganic acid fluoboric acid with or without boric acid is utilized when the tin salt is stannous fluoborate. Except in those baths containing stannous fluoborate, the baths usually contain an acid of the same kind as the acid radical or anion of the tin salt, i.e. an acid having the same anion as the anion of the tin salt, for instance sulfuric acid when stannous sulfate is utilized, and hydrochloric acid when stannous chloride is the tin salt.

The preferred operating conditions for obtaining the bright, level tin electrodeposits herein are a bath temperature in the range of about 25 C.-35 C., and a current density in the range of about 2.540 amp/sq. ft. The pH of the tin electrodeposition baths herein are preferably in the range from 0.0 to 1.5.

A preferred amount of the cyclohexylsulfamate for use herein as the brightening and levelling agent is in the range of about 0.1-1 gram thereof per liter of bath.

A preferred very bright, high levelling tin electroplating bath herein comprises an aqueous acidic solution containing the following constituents within the approximate ranges specified:

Stannous sulfate g./l 50-100 Sulfuric acid ml./l 2050 Orthocresolsulfonic acid g./l 5O Alkali metal cyclohexylsulfamate g./l 0.1-1

The sulfuric acid in the above formulation is concentrated sulfuric acid, and specifically was 66 B. acid.

The primary brightener and grain refiner is preferably a cresolsulfonic acid, for example o-cresolsulfonic, or a phenolsulfonic acid, for example oand p-phenolsulfonic acid. These hydroxy aromatic sulfonic acids are obtainable in commerce. However it is to be understood that any bath-compatible primary brightener and grain refiner is utilizable in the tin electrodepositing bath in the preferred embodiments of this invention in combination with the cyclohexylsulfamate as secondary brightener which will yield a considerable improved brightness, level tin deposit, and which is a nonbrittle, low stress, ductile tin deposit. Primary brighteners and grain refiners are well known in the metal electroplating art as additives which impart brightness and ductility to the metal deposit. Primary brighteners are used in the prior art in combination with secondary brighteners to yield a metal deposit of appreciably improved brightness over the use of the primary brightener alone and which is a non-brittle, ductile deposit. The secondary brighteners, as known in the prior art, utilized alone in the plating bath impart brighteners to the metal deposit but tend to yield a brittle, excessively stressed deposit. By bath compatible as used herein in describing the secondary brightener is meant a secondary brightener which will not substantially detrimentally or adversely affect the acid tin electrodepositing bath, as an ingredient thereof for the purpose of imparting brightness and ductility to the tin electrodeposit.

In another embodiment, the present invention comprehends an acid composition suitable for use in bright, levelling tin electroplating. More specifically the acid composition of this embodiment is a concentrate adapted for admixing with an aqueous liquid, for instance water, to form an aqueous acid tin electrodepositing bath and comprising a mixture of a water-soluble tin salt, for instance a water-soluble stannous salt, an acid, usually an inorganic acid such as a mineral acid, a compatible primary brightener and grain refiner which is preferably a cresolsulfonic acid or a phenolsulfonic acid, and as a secondary brightened and levelling agent a cyclohexylsulfamate of the formula previously set forth herein. Typical proportions of ingredients in such concentrate are, by weight, from about 33-75% of the soluble tin salt, from about 12-45% of the acid, from about 0.05-1.25 of the cyclohexylsulfamate, and from about 740% of the primary brightener and grain refiner. Percentages of ingredients are based on the total composition or concentrate. The acid is usually one having the same anion as the anion of the stannous salt.

In still another embodiment the present invention provides additive compositions which are eminently well suited for use as brighteners and levelling agents in aqueous acid tin electroplating baths. One additive composition herein eminently well suited for use as a brightener and levelling agent in the acid tin electroplating baths comprises a mixture of a water-soluble tin salt, for instance a water-soluble stannous salt, and a cyclohexylsulfamate of the formula previously disclosed herein. The proportions of the ingredients of the last-mentioned additive are, by weight, from about 0.1-2% of the cyclohexylsulfamate, and the remainder the soluble tin salt. Another additive composition of this invention which is well suited as a brightener and levelling additive for acid tin electroplating baths is composed of a mixture of the water-soluble tin salt, for instance the stannous salt, the cyclohexylsulfamate of the formula aforesaid, and the acid. Typical proportions of the ingredients of such additive compositions are, by weight, from about 5082.5% of the soluble tin salt, from about 0.071.5% of the cyclohexylsulfamate, and the remainder the acid. Still another additive composition herein is a mixture of the primary brightener and grain refiner and the cyclohexylsulfamate of the formula aforesaid with or without the inorganic acid. Typical proportions of the ingredients of the last mentioned additive composition when the acid is present are, by weight, from about 17-70% of the primary brightener and grain refiner, from about 0.13% of the cyclohexylsulfamate as secondary brightener and leveller, and the remainder the acid. Such additive composition is also well suited as a brightening and levelling additive for acid tin electroplating baths.

The proportions of ingredients of the additive compositions of this invention are not especially critical and can be varied over fairly wide ranges having upper and lower percentage limits appreciably above and below those of the corresponding additive compositions previously disclosed herein. In adding an additive composition of this invention to an already prepared acid tin electroplating bath or for mixing together with other bath ingredients during the formulating of the plating bath, proper allowance should be made for ingredients already in the bath, for instance the soluble tin salt, mineral acid, or primary brightener, when such ingredient or ingredients are also present in the additive, so that the amounts of the ingredients in the final plating bath are within the particular quantity limits desired.

The following examples in the table which follows are of tin electroplating baths of this invention which provide very bright and levelling tin deposits.

Cyclo- Orthohexylcresol- Stannous H2804 sulfamsulionic sulfate, (66 Be) ate, acid, g. l. ml./l. g./l. g./l.

The cyclohexylsulfamate of Examples 14 of the table was sodium cyclohexylsulfamate. The baths of Examples 1-4 were at a temperature of about 25 C.30 C. during the electrolyzing and with a current density of about 5 to 40 a./ft.

The following examples further illustrate the invention with respect the additive compositions herein:

EXAMPLE 5 Percent by weight Sodium cyclohexylsulfamate 1 Stannous sulfate 99 EXAMPLE 6 Sodium cyclohexylsulfamate 0.1

Stannous sulfate 99.9

EXAMPLE 7 Potassium cyclohexylsulfamate l Stannous fluoborate 99 EXAMPLE 8 Sodium cyclohexylsulfamate 0.8

Stannous sulfate 65.0

Sulfuric acid (66 B.) 34.2

EXAMPLE 9 Sodium cyclohexylsulfamate 1 Stannous fluoborate 66 Fluoboric acid 33 EXAMPLE 10 Calcium cyclohexaylsulfamate 2 Stannous chloride 98 EXAMPLE l1 Stannous cyclohexylsulfamate 0.5

Stannous chloride 99.5

EXAMPLE 12 Sodium cyclohexylsulfamate 1 Sulfuric acid (66 B.) 60

Orthocresolsulfonic acid 39 What is claimed is:

1. In a process for electrodepositing tin from an aqueous acid tin electrodepositing bath comprising an aqueous acid solution of a water-soluble stannous salt and a primary brightener, the improvement which comprises electrodepositing the tin from the bath also having present therein during the electrodepositing a secondary brightener and levelling agent consisting essentially of an effective amount, sufficient to yield an appreciably brighter, level tin electrodeposit, of a cyclohexylsulfamate of the formula S NHSO M wherein M is selected from the group consisting of hydrogen, alkali metal, alkaline earth metal and divalent tin, the bath yielding the brighter level tin deposit without requiring melting and refiowing of the tin electrodeposit.

2. The process of claim 1 wherein M is a bath-compatible, water-sodlubilizing alkali metal cation.

3. The process of claim 2 wherein the alkali metal cation is Na' 4. The process of claim 1 wherein the electro-depositing is conducted at a bath temperature in the range of about C.- C. and a current density in the range of about 2.5- amperes per square foot.

5. The process of claim 1 wherein the cyclohexylsulfamate is present in the bath in amount in the range of about 0.1-1 gram per liter of bath.

6. In an aqueous acid tin electrodepositing bath containing a bath soluble stannous salt and a primary brightener, the improvement which comprises having present in the bath a secondary brightener and levelling agent consisting essentially of an effective amount, sufficient to yield an appreciably brighter, level tin electrodeposit, of a cyclohexylsulfame of the formula wherein M is selected from the group consisting of hydrogen, alkali metal, alkaline earth metal and divalent tin, the bath yielding the brighter, level tin deposit without requiring melting and refiowing of the tin electrodeposit.

7. The bath of claim 6 wherein M is a bath-compatible water-solubilizing alkali metal cation.

8. The bath of claim 7 wherein the alkali metal cation is Na+.

9. The bath of claim 1 wherein the cyclohexylsulfamate is present therein in amount within the range of about 0.1-1 gram per liter.

10. An aqueous acid tin electroplating bath for producing level, ductile tin electrodeposits of appreciably improved brightness comprising an aqueous acidic solution consisting essentially of the following constituents within the proportion ranges hereafter specified:

Stannous sulfate-about 50-100 g./l.

Sulfuric acid (66 B.)ab0ut 20-50 ml./l. Orthocresolsulfonic acid-about 10-50 g./l.

Alkali metal cyclohexylsulfamate-about 0.1-l g./l.

the bath yielding the brighter, level ductile tin deposit without requiring melting and reflowing of the tin electrodeposit.

11. An additive compositon for tin electroplating baths consisting essentially of a mixture of a primary brightener for the tin, and as a secondary brightener and levelling agent for the tin a cyclohexylsulfamate of the formula wherein M is selected from the group consisting of hydrogen, alkali metal, alkaline earth metal and divalent tin.

12. The additive composition of claim 11 wherein the primary brightener is selected from the group consisting of a cresolusulfonic acid and a phenolsulfonic acid.

13. The process of claim 1 wherein the primary brightener is selected from the group consisting of a cresolsulfonic acid and a phenolsulfonic acid.

14. The bath of claim 6 wherein the primary brightener is selected from the group consisting of a cresolsulfonic acid and a phenolsulfonic acid.

References Cited UNITED STATES PATENTS 2,870,070 1/1959 Higgs et al. 204-54 3,023,150 2/1962 Willmund et al 204-44 FOREIGN PATENTS 828,200 2/ 1960 Great Britain. 1,030,209 5/ 1966 Great Britain.

DANIEL E. WYMAN, Primary Examiner C. F. DEES, Assistant Examiner 2 33 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 979 259 Dated November 18, 1969 Inventor(s) Raymond F Nambride It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' Column 5, line 58, "water-sodlubilizing" should read --water-so1ubi1izing--.

Column 6, Line 7 "cyclohexylsulfame" should read --cyclohexysu1famate--.

SIGNED 'KND SEALED JUN9 1970 (SEAL) Attest:

Edward M. Fletcher, Ir. wmmm E. 5.0mm.

Attesting Officer Commissioner of Pawn 

